Remotely adjustable switch



Oct. 4, 1960 V. C. WESTCOTT EAL REMOTELY ADJUSTABLE SWITCH Filed June 10, 1957 F l G. I

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WESTCOTT WILLIAMS ATTORN EYS.

VERNON SIDNEY United States Patent OfiFice Patented Oct. 4, 1960 REMOTELY ADJUSTABLE SWITCH Vernon C. Westcott, Lincoln, and Sidney B. Williams, Lexington, Mass, assignors to Trans-Sonics, Inc., Lexington, Mass.

Filed June 10, 1957, Ser. No. 664,812

17 Claims. (Cl. 200-81) This invention relates to a remotely adjustable switch. More particularly, it relates to a novel construction for an adjustable pressure-operated switch which may be remotely adjusted to operate at a particular pressure.

Switches responsive to pressure, temperature, magnetic field, etc., have previously been made which are adjustable so that they operate at a particular value of the force-producing agency which actuates them. In general, adjustment to operate at this particular value is accomplished by mounting the fixed or non-actuated contact of the switch on a support whose position is adjustable with respect to the movable contact. Usually the contact support is mounted on a threaded shaft or the like. Rotation of this shaft, which passes through a fixed nut or tapped opening, moves the fixed contact toward or away from the movable contact when rotated. In general, the position of the fixed contact determines the amount of force required to cause the switch to close or the level below which the actuating force must drop before the contacts disengage. Thus the closing or opening level of force and therefore the value of the forceproducing agency is determined by the rotation of the threaded shaft.

While this construction is satisfactory when the switches are accessible for adjustment, there are certain applications where they must be adjusted from a remote location. Thus, in certain industrial applications adjustable switches responsive to pressure, temperature, etc., are located in remote and sometimes inaccessible locations. For example, pressure controlling switches in nuclear power plants often cannot be reached because of the radiation hazard. in the past, once these switches were installed, they could only be adjusted through the use of relatively expensive high precision servo systems. In many applications pressure-operated switches of this type must operate in atmospheres which may degrade switch operation. Thus the surrounding atmosphere may be dirty, which will impair both the mechanical and electrical operation of the switch, or the atmosphere may be moisture-laden, which will cause arcing, etc., at the switch contacts. Further, in many industrial and aircraft applications, remotely adjustable switches must operate in areas of high ambient vibration. In such use it is desirable that the switch be rugged and free from lowfrequency resonances, which might cause contact chattering.

Accordingly, it is a general object of our invention to provide an improved remotely adjustable switch. A more particular object of our invention is to provide a switch of the type described which may be remotely adjusted by supplying it with the appropriate force-producing agency at the level at which the switch is to operate, thereby eliminating the need for an expensive servo system. A further object of our invention is to provide a pressureoperated switch of the type described which may be remotely adjusted by supplying a regulated calibrating pressure thereto. Another object of our invention is to provide a switch whose closing or opening may be individually adjusted, even when it is fed by the actuating agency in common with other switches of the same type. Still another object of our invention is to provide a switch of the character described which will retain calibration after adjustment. Still another object of our invention is to provide a switch of the character described which will operate in areas of high ambient vibration, such as are encountered in aircraft and missiles. A still further object of our invention is to provide a pressure-actuated switch of the character described which may be hermetically sealed, not only from the surrounding atmosphere but also from the fluid actuating the pressure-operated portion thereof. A still further object of our invention is to provide a switch of the character described which is simple, inexpensive, and rugged in construction. Other and further objects of our invention will in part be ob vious and will in part appear hereinafter.

The invention accordingly comprises the features of construction, combinations of elements, and arrangements of parts which will be exemplified in the constructions hereinafter set forth, and the scope of the invention will be indicated in the claims.

For a fuller understanding of the nature and objects of our invention, reference should be had to the following detailed description taken in connection with the accompanying drawings in which:

Figure 1 is a vertical section of an embodiment of a pressure-operated switch made according to our invention and taken along the line 11 of Figure 2,

Figure 2 is a top plan view of the switch of Figure l with the cases removed to show the construction of the switch and associated mechanism,

Figure 3 is a fragmentary section through the clutch mechanism of the switch illustrated in Figures 1 and 2 taken along the line 3-3 of Figure 2, and

Figure 4 is a section through the shaft and mounting of the movable contact of the switch, illustrating an alternative clamping arrangement.

Briefly, as seen in Figures 1 and 2, our switch includes a pressure-responsive portion generally indicated at 10, the switch itself generally indicated at 12, and a clamping or locking device for the fixed contact generally indicated at 14. (Figure 2). The pressure-responsive portion 10 includes a sealed bellows 16 which is springloaded by a reference coil spring 18 inserted between the top of the bellows and the plate 20 on which the switch 12 is supported. Pressure admitted to the interior of the bellows causes it to move upwardly as seen in Figure 1 against spring 18, and this motion is utilized to rotate the pivoted arm 22 which carries thereon movable contact 24. The fixed contact 26 of the switch is supported on a rotatable bracket 28, this bracket being supported on a shaft 36 which in turn is clamped in a releasable clamping block 32 (Figure 2). A hair spring 34 in tension is connected between bracket 28 and plate 20; therefore, as block 32 is unclamped, the fixed contact 26 is urged into engagement with the movable contact 24. Electrically-operated clamping means generally indicated at 36 is provided to release shaft 30 and thus allow the switch to close at the proper time during calibration.

To set the switch to close at a particular pressure, the clamping device 36 is energized, releasing the fixed contact 26 so that it moves under the urging of the spring 34 into engagement with the movable contact 24. A regulated pressure which is close to the value at which the switch is to operate is then supplied to the bellows 16, and this rotates arm 22 carrying contact 24- to a position corresponding to the applied pressure. Since the force exerted by the bellows 16 and the arm 22 is much larger than that exerted by hair spring 34, the movable contact carries the fixed contact with it to the new location. With the calibrating pressure still applied, the clamping device 36 is de-energized, and the calibrating pressure may then be removed. Thereafter, whenever a pressure equal to the calibrating pressure is applied to the switch, the switch contacts will be closed with a contact pliessureequalto the force e e e by the ha spr n during calibration, Wh tsi i s r d. to av the contacts bar y touch at a iven app e p e sur it is e rable to supp y a sligh y higher pressure for calibration than that at which the on ac b e y .touc

After the clamping device is set, the calibrating pressure is removed and normal pressure is applied. If the normal pressure is below the calibrating pressure, an increase in this pressure will cause the ,switchto operate, i.e., the contacts will touch at a pressure just below the pressure to whichthe switch was calibrated. Similarly, if the normal applied pressure is above the calibration prcssure, the switch Will open at a pressure just below the calibration pressnre as the applied pressure decreases.

Mo e nep fi ally as e n n Figu e 1, t pressure switch embodying our invention includes a circular base or header 37 with a boss 38 integrally formed on its lower surface. A passage 39 fortlie admission of fluid to the inter or of the bellows is formed in the boss the base nd. si terha y h e d as at 394 th a ta a Pr ssure thread. A plurality of hermetic terminals such as terminal ail arernountedin the base 37 to provide ole"- trieal connections to the switch contacts and the clamping evi e f om t e utsi e- The bellows assembly includes the bellows 16, a lower adapter s L'which hermetically seals the lower end of the ellows t9 e base 0, d a s g sk 42 which hermetically seals the top of the bellows. In this manner the fluid which is to actuate, the switch is admitted to the bellows interior only, and the switch with its associated supports and clutching mechanism may be sealed from the effects of dirt, moisture, etc., both in the surrounding atmosphere and in the actuating fluid. .A line mesh screen 43 is supported on the lower end of adapter 41 to prevent large particles of dirt, etc., from entering the bellows.

The lower end of reference coil spring 18 is seated in a depression 42a formed in the upper surface of sealing isk 42, while. its upper end seats against a spacer 44 in a counterhore 45 in supporting plate 20. This reference Spring is, selected to have a spring constant which, when combined. with the spring constant of the bellows, will provide the desired pressure, range for the switch. The reference springalso'increases the spring constant of the entire pressureractuated portion of the switch, providing a n tural. frequency in excess of one hundred cycles per second. Thus: the switch can follow rapid changes in applied pressures. Because the. reference spring 18. has a spring constant which is much higher than .that of the bellows 16, any small hysteresis effects in the spring constantof the bellows will have a negligible effect on overall switch performance. Also, since the spring 18 is outside the bellows rather than sealed within it, as is the usual practice, the bellows assembly is easier. to fabricate and linear operation. may be. more readily attained. Since the bellows 16 andfthe. reference. spring 18 are separate components, the design of. each of these. elements may be. optimized, i.e., the. most desirablebellows may be. selected with reference to. such considerations as material, number of.convolutions, etc., and a reference, spring may. be selected. which optimizes the overall; instrument performance.

The support plate20 is attached. to thebase. 37 by three, supportposts 4.6, 47 and 48. (.post 48. being omitted. in Figurel fonpurposesofclarity). Theheight of the plate 20.a'bove thebase 37 is set accurately to. withinvery close tolerances by these posts, since thisheight. and the thickness of spacer. 44. determine. the amount. of. compression ofthespring 18. and bellows 16 and thereforethepressure range of the switch.

As shown in Figures 1 and 2, a bearing bracket 50 is screwed to the upper surface of the plate 20 and pivotally supports the arm 22 carrying the movable contact 24. This bearing bracket 50 has a rectangular base member 50a with integral bearing blocks 50b upstanding therefrom. The arm 22 is fixed to a shaft 52, the ends of the shaft 52 being journelled in the bearing blocks 50b. A threaded circular rod 54 is formed on the outer end of arm 22 and carries thereon a counterweight 56. A threaded passage 5.6a extends through the center of counterweight 56 so that its position may be adjusted along the rod. The counterweight position is adjusted during manufacture by subjecting the switch to oscillatory motion to provide high acceleration forces and then adjusting the counterweight to minimize the motion of arm 22 as a result of this motion. The movable contact 24, mounted on the upper surface of rotatable arm 22, is insulated therefrom by a disk 58 of insulating material. The contactmay be of any of the conventional materials, such s p lladium, used for uch p p ses.

A thing elastic berylliumrcopper link 59, which is so shaped that it will operate for many cycles without tigu g, conne ts he inner nd of arm 2.2 to a proi cticn 6. a forme en he. upper e d of apos 60 hich is integral'with sealing disk 42,- This linkage transmits the motion of the pressure-actuated portion of the instrumen to e arm 2.

The. fix d C n t 6 f swi ch 2 i mo nted n h -rs aped b ac t 28 ith an sula ng disk 62 between he on act nd, h b acke e racke i a c as by screws onthe like, to the bracket support block 64, whi h i tu n. i fixed to one dv f sh t Th o h r nd of he sha 36 e tsn s h c gh b e n the shaf upp rt br cket 32 as c at d w e c amp g device 14-. As es e n in F gure 3, e b e formed in the uppo b ck sl ted a a 24 o t at h bore y e li htly nlarg d y pre ng he o to pe i shaft 30 to rotatefreely therein. When the slot is not so spread, the shaft 30. is sealed tightly therein to lock it and the fixed contact at a particular location. A plate 68 of magnetic material which may be integral with one side of the bracket 32 forms. with the L-shaped bracket extension 32b a magnetic circuit having an air gap 320. Coil 7i) wound on the plate 68 causes the plate 63 to move to close the air gap 320 when it is energized. This motion spreads the slot 3241, thus enlarging the bore in the bearingbracket to permit shaft 30 to rotate under the influence of the hair spring 34 and fixed contact 26 to engage movable contact 24.

An alternative clamping arrangement which may be used to clamp the fixed contact structure is illustrated in Figure 4, which is a vertical section through. the bracket 32 and the shaft. 3100f this clamp. In this arrangement the bracket 32 is neither slotted nor is it provided with the l -s haped extension 32b or plate 68. Rather, at operating temperatures the shaft 30 is a force fit in the bore provided in the bracket 32 and is held with sufficient force to prevent its rotation. The shaft 30 is made of a material having a low coeflicient of expansion with temperature, such as steel or Invar, while the bracket is made. of a material having a high coefficient of expansion with temperature, such as aluminum. A coil 72 of resistance wire encircles the bracket 32 and when energiz ed heats both the bracket and shaft. Since the bracket 32 has a higher coefficient of expansion than the shaft 30, the bore therein .willexpand faster than the shaft when heated above its operating temperature, allowing the shaft to rotate under the influence of the hair spring 34. When the coil 72 is. de-energized, the bracket and shaft cool to operating temperature, the, bracket contracting at a fasterrate than the shaft to again lock the aft T rn n gain to gur s. 1\ a d r ded, r d. 74

similan to rod: 54; and; a. counterweight. 76. similar toweight- 56: are. provided. on. bracket support block 64. to

minimize the efiect of vibration on the fixed contact when the clamping device is energized.

While we have described a pressure switch in which the motion of the fixed contact under the influence of hair spring 34 is limited by its engagement with the movable contact, it is apparent that the two functions performed by the movable contact, i.e., that of a contact and that of a stop, could each be performed by two separate parts. In such a construction a stop attached to the movable contact rather than the contact itself would engage some portion of the fixed contact structure. in this manner the switch could be adjusted to limit its movement to operate at a pressure different from that supplied during calibration by some fixed amount.

Further, while we have described our pressure-operated switch in connection with a spring and bellows construction, it will be apparent that other pressure-sensitive devices, e.g., a Bourdon tube, might be used to change the applied pressure into a displacement. Similarly, temperature sensitive devices might be used to operate the switch directly, and many types of electrically operated switches might be incorporated within the inventive concept.

As shown in Figure l, the entire switch assembly is enclosed in an inner case 78 which may be hermetically sealed to the base 37. If the switch is to be responsive to absolute pressure, this case may be evacuated. If the switch is to respond to differential pressure, a fluid passage (not shown) is provided to the interior of this case; a sintered metal filter is usually inserted in this passage to prevent the entry of dirt or other foreign materials to the switch interior.

The aluminum outer case 80, of substantially heavier material than the inner case 78, is provided to protect the instrument from damage and may be affixed to the base in any convenient fashion. A plastic terminal guard 82 may also be provided to prevent damage to the hermetic terminals, such as terminal 40 in the base 37.

To remotely adjust a single switch made according to our invention, the clamping device, which may be either the magnetic or the thermal type described or other types which will be apparent to those skilled in the art, is released, allowing fixed contact 26 to rotate to engage a stop under the influence of hair spring 34. As described, this stop may be the movable contact itself or structure attached to the movable contact support. A regulated pressure is then supplied to the bellows 16 through the passage 39. This pressure causes the bellows to expand against the reference spring 18, and the bellows motion is transmitted by post 60 and link 59 to pivoted arm 22. Arm 22 rotates carrying movable contact 24 with it to a position corresponding to the applied pressure. In so doing it also causes movement of the fixed contact which is in contact therewith. When the switch has settled to a position, the clamping mechanism is de-energized and the calibrating pressure is removed, adjustment having been completed. Where a plurality of switches are supplied from a common pressure line, each switch may be individually adjusted to operate at different pressures by individually energizing the clamping devices when the common line is supplied with the desired calibrating pressure.

If a plurality of switches are to be remotely adjusted in a missile, for example, a pressure supply line may be connected between the missile pressure port and a block house at the launching site. A plurality of regulated pressure sources may be manifolded to this line in the block house, each being connected to the manifold through a solenoid valve. The leads connected to the individual switch clamping devices may also be brought to the block house via the missile umbilical cord. Then by setting the individual pressure sources to the desired values, the solenoid valves and the clamping devices may be simultaneously energized and de-energized either manually or automatically to completely and accurately calibrate all the switches in the missile.

Thus We have provided an improved adjustable switch which may be set from a remote location to operate at a particular level of the force-producing agency, i.e., pressure, temperature, magnetic field, etc., which actuates it. This switch is relatively inexpensive and does not require the expensive and heavy servomechanisms previously used to adjust such switches; rather, it requires only two leads to energize a simple clamping device contained within the switch. We have described as one embodiment of our invention a pressure-operated switch which may be hermetically sealed to serve as an absolute device or which may operate on a pressure differential. When hermetically sealed, the switch operates in a vacuum and 1 is isolated from dirt, moisture, or corrosive fluids, including the fluids used to actuate it. Because of its construction the switch is resistant to vibration and will operate to follow rapidly varying pressure changes.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efiiciently attained and, since certain changes may be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

We claim:

1. A remotely adjustable switch comprising, in combination, a fixed contact, a movable contact, means adapted to move said movable contact into engagement with said fixed contact, means adapted to urge said fixed contact toward said movable contact, means for limiting the movement of said fixed contact toward said movable contact, clamping means for locking said fixed contact at a particular location, means for releasing said clamping means to permit said means for urging said fixed contact to move said fixed contact into engagement with said limiting means, and means for reengaging said clamping means to lock said fixed contact in such position, thereby to determine the travel of said movable contact required to operate said switch.

2. A remotely adjustable switch comprising, in combination, a fixed contact, a movable contact, means adapted to move said movable contact from an initial position into engagement with said fixed contact, impositive means adapted to urge said fixed contact into engagement with said movable contact, clamping means for locking said fixed contact at a particular location, means for releasing said clamping means to permit said impositive means to urge said fixed contact into engagement with said movable contact, and means for reengaging said clamping means to lock said fixed contact in such position, whereby said movable contact may be positioned at any point along its path of movement and said fixed contact may be fixed at said point, thereby to determine the travel from said initial position to said fixed contact for operation of said switch.

3. A remotely adjustable pressure-operated switch comprising, in combination, a fixed contact, a movable con tact, pressure-sensitive means adapted to move said movable contact into engagement with said fixed contact, resilient means adapted to urge said fixed contact into engagement with said movable contact, clamping means for locking said fixed contact at a particular location, and means for releasing said clamping means to permit said resilient means to urge said fixed contact into engagement with said movable contact, whereby a predetermined pressure may be applied to said pressure sensitive means to locate said movable contact at a point along its path of travel and said fixed contact may be locked for engagement with said movable contact at said point, thereby to adjust said switch for operation at said predetermined pressure.

4. The combination defined in claim 3 in which said pressure-sensitive means includes a spring-loaded bellows.

5. The apparatus defined in claim 4 in which said spring loading said bellows is located outside said bellows.

6. A remotely adjustable pressure operated switch comprising, in combination, a base having a passage therein, a closed bellows sealed to said base-over said passage, whereby fluid may be admitted to the interior of said bellows through said passage, said bellows expanding and contracting in response to changes in fluid pressure, a fixed switch support plate, means mounting said switch supportplate spaced from said base and said bellows, a reference spring interposed between said support plate and said bellows, said spring being compressed upon expansion of said bellows, a first arm pivotally mountedon said switch support plate, a linkage connecting said arm and said bellows, whereby said first arm is rotated by the motion of said bellows, an electrical contact mounted on said first arm, a second pivotally mounted arm, an electrical contact carried by said second arm, clamping means for locking said second arm at a fixed location, said clamping means being releasable upon excitation by an electrical signal, and a spring between said plate and said second arm to urge said electrical contact mounted thereon into engagement with said electrical contact mounted on said first arm when said clamping means is released.

7. A remotely adjustable switch comprising, in combination, a fixed switch supporting member, a first arm pivotally mounted on said switch supporting member, switch operating means adapted to rotate said first arm about its pivot in response to an input signal, an electrical contact mounted on said first arm, a second pivotally mounted arm, an electrical contact carried on said second arm, resilient means connected between said second arm and said supporting member to urge said contact on said second arm into engagement with the contact on said first arm, clamping means for locking said second arm at a fixed location, means for releasing said clamping means to permit said resilient means to move said contact on said second arm into engagement with said contact on said first arm, and means for re-engaging said clamping means to lock said arm, whereby said switch operating means may be operated to rotate said first arm to bring said electrical contact mounted thereon to a given location corresponding to a predetermined input signal to said I operating means, and said contact on said second arm may be locked at said location, thereby to determine the input signal required for operation of said switch.

8. The combination defined in claim 7 in which said switch operating means is pressure sensitive.

9. The combination defined in claim 7 in which-said switch operating means includes a spring loaded bellows which converts variations in fluid pressure applied thereto to linear motion.

10. A remotely adjustable switch comprising, in combination. a fixed contact, a movable contact, a force producing agency adapted to move said movable contact into engagement with said fixed contact, means mounting said fixed contact on a shaft for rotation therewith, clamping means for said shaft including a bracket having a bore formed therein for supporting said shaft, said shaft being a force fit in said here and means for enlarging said: bore to permit said shaft to rotate therein, resilient means adapted to rotate said shaft in said here and. thereby urge said fixed contact into engagement with said movable contact, whereby said force producing agency may be operated. to produce a predetermined force and movesaid movable contact. to a given positionv and said clamping means may be operated to permit said fixed. contact to bev moved by said resilient means against said movablecon' tact and to clamp said fixed contact tliereat, thereby to determine the force required to move said movable contact into engagement with said fixed contact.

11. A remotely adjustable switch comprising, in combination, a fixed contact, a movable contact, a forceproducing agency adapted to move said movable contact into engagement with said fixed contact, means mounting said fixed contact on a shaft for rotation therewith, clamping means for said shaft includes a bracket having a bore formed therein for supporting said shaft, said shaft being a force fit in said bore, said bracket being slotted along said bore, a solenoid adapted to spread said slot when energized, thereby to enlarge said bore to permit saidshaft to rotate therein, andresilient means adapted to rotate said shaft in said bore and urge said fixed contact into engagement with said movable contact, where- .by said force-producing agency may be operated to produce a predetermined force and move said movable contact to a corresponding location and said solenoid may be energized to permit said resilient means to move said fixed contact into engagement with said movable contact, whereupon de-energization of said solenoid clamps said fixed contact at said location to determine the force required to move said movable contact into engagement with said fixed contact.

12. A remotely adjustable switch comprising, in combination, a fixed contact, a movable contact, a force-producing agency adapted to move said movable contact into engagement with said fixed contact, means mounting said fixed contact on a shaft for rotation therewith, clamping means for said shaft including a bracket hav ing a bore formed therein for supporting said shaft, said shaft being a force fit in said bore, said bracket being of a material having a higher coefficient of thermal expansion than said shaft, means for heating said bracket thereby to enlarge said bore and release said shaft for rotation therein, and resilient means adapted to rotate said shaft in said bore and urge said fixed contact into engagement with said movable contact, whereby said force-producing agency may be operated to produce a predetermined force and move said movable contact to a corresponding location and said bracket may be heated to permit said resilient means to move said fixed contact into engagement with said movable contact, whereupon said bracket may be cooled to clamp said fixed contact at said location thereby to determine the force required to move said movable contact into engagement with said fixed contact.

13. In a device providing an electrical output signal which is a function of the position of a first movable elc' ment with respect to a reference point, the combination of operating means adapted to move said movable element relative to said reference point in response to an input signal, adjusting means adapted to adjust the relative positions of said movable element and said reference point, said adjusting means comprising an adjusting member, impositive means adapted to move said member independently of said input signal, first stopping means having a fixed position relative to said reference point, second stopping means having a fixed position relative to said movable element, said impositive means urging said stopping means into engagement with each other, locking means for locking said adjusting member against movement by said impositive means, and means for releasing said locking means, whereby a predetermined input signal may beapplied to said operating means to position said movable element at a given point associated with such signal, said locking means may be released to permit said impositive means to bring said first and second stopping means into engagement with each other and said locking means may then be locked to fix the position ofof a first movable element with respect to a reference point, the combination of operating means adapted to move said movable element relative to said reference point in response to an input signal, adjusting means adapted to adjust the relative positions of said movable element and said reference point, said adjusting means comprising an adjusting member including first stopping means, said reference point having a predetermined re lationship to the position of said adjusting member, said operating means including second stopping means, impositive means adapted to urge said adjusting member to move and bring said first stopping means against said second stopping means, thereby to stop said adjusting member, locking means adapted to lock said adjusting member against movement by said impositive means, means for releasing said locking means, and means for relocking said locking means, whereby the position of said reference point may be adjusted to calibrate said device by applying a predetermined input signal to said operating means, releasing said locking means to move said first stopping means against second stopping means and obtain a predetermined relationship between said movable element and said reference point, and relocking said locking means to maintain said reference point in its position.

15. In a device adapted to produce an electrical output signal which is a function of the distance between a movable electrode and a fixed electrode, the combination of a first unit including said movable electrode, a second unit including said fixed electrode, operating means adapted to move said movable electrode relative to said fixed electrode in response to an input signal, adjusting means independent of said operating means urging relative movement of said units toward each other, locking means for looking said units against the action of said adjusting means, and means for releasing said locking means whereby a predetermined input signal may be applied to said operating means to position said first unit at a given point, said locking means may be released to permit said adjusting means to move said units into engagement with each other and said locking means may be relocked. thereby to determine the distance between said electrodes as a function of said input signal and calibrate said device.

16. An adjustable switch comprising, in combination, a first unit including a movable contact, a second unit including a fixed contact, switch operating means adapted to move said movable contact into engagement with said fixed contact, adjusting means independent of said op- :erating means urging relative movement of said units toward each other, locking means for locking said units against the action of said adjusting means, means for releasing said locking means, and means for relocking said locking means, whereby said switch may be adjusted by actuating said operating means to position said movable contact at a predetermined point and said locking means may be released to permit said adjusting means to move said units into engagement with each other and then relocked, thereby to determine the travel of said movable contact required for operation of said switch, said contacts being fixed with respect to the remaining portions of the respective units in which they are included during adjustment of said switch.

17. The combination defined in claim 16 in which said contacts are the engaging portions of said units.

References Cited in the file of this patent UNITED STATES PATENTS 951,259 Rolfe Mar. 8, 1910 1,952,050 Bast Mar. 27, 1934 2,532,265 Zickrich Nov. 28, 1950 2,707,217 Collins et al. Apr. 26, 1955 2,712,576 Gibson July 5, 1955 2,755,362 Jacobs July 17, 1956 2,803,722 Kuhn Aug. 20, 1957 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent Non 2,955 172 October 41. 1960 Vernon Cu Westcott et ala It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4 line 6 for joulrnelled read journalled -===g line 20, for "thing" read thin column 6, lines 44 and 57, for "reengaging" each occurrence read re -engaging column 8 line 8, for "includes'" read including column 1O line 4 for "'relooked," read relocked a Signed and sealed this 11th day of April 1961,

(SEAL) Attest:

ERNEST" W. SWIDER ARTHUR w. CROCKER Attesting Oflicer Adina Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N00 2,955 l72 October M 1960 Vernon Co Westcott et al.,

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4 line 6 for "journelled" read journalled line 20 for thing read thin column 6 lines 4% and 57, for '"reengagingM each occurrence read re 'engaging column 8,, line 8 for includesread including column 10 line 4, for "relockedfl" read relocked Signed and sealed this 11th day of April 1961.,

(SEAL) Attest: I

ERNEST W. SW IDER ARTHUR w. CROCKER Attesting Officer Acting Commissioner of Patents 

